Foundry composition and method



Patented Apr. 8, 1941 FOUIdDRY COMPOSITION AND METHOD Norman J. Dunbeck,Eifort. Ohio, assignor to Peerpatco, Incorporated, a corporation ofDelaware NG DI'EWiDI- Original application November 27, 1939, Serial N0,308,392. Divided and m8 Ilia plication December 16, 1940, Serial No.370,421

7 Claims.

My application for patent is a division of my copending applicationSerial No. 306,392, filed November 27, 1939, and entitled Foundrycomposition and method, and the invention relates to compositions ofmatter, and especially to compositions for foundry use.

Among the objects of my invention are the V provision of a foundrycomposition which 'is strong yet permeable tothe fumes and gasesencountered in actual use; which may be readily and accurately prepared,so as to have any desired dry strength according to the needs of theparticular type of casting being made; which, at the same time, has asatisfactorily high green strength and a high sintering point; and whichdoes not cake or harden in use so that it may be easily recovered forrepeated use.

Another object of my invention is to provide a foundry composition asdescribed above, which can be prepared from readily available and inexpensive materials.

Other objects will be in part obvious and in a part pointed outhereinafter.

The invention accordingly consists in the combination of elements,mixture of materials and composition of ingredients, and in the severalsteps and the relation of each of the same to one or more of the othersas described herein, the scope of the application of whichis indicatedin the following claims.

In present foundry practices, a small amount of bonding clay is added toclean silica sand which is tempered with water to form a moist workablemass. The clay may be blended either with clean sand or with a mixtureof clean and burnt sand. In forming a mold; this composition is rammedabout a pattern placed within a molding flask. The clay present in theblend gives strength to the mold so that it retains its shape when theflask is separated to remove the pattern. The clay also enables the moldto resist erosive action ofthe molten metal poured into it and tosupport the weight of that metal;

Both fire clays and non-refractory clays have been used forthis purpose,but these clays are not satisfactory. In order to make amold ofsatisfactory strength, between 10% and 30% of this type of clay must beused, depending upon the quality of the sand, the quality of the clayand the weight of the casting being made. Such a large quantity of claytends to severely curtail the permeance of the mold. This porosity orpermeance is essential to a proper elimination of fumes evolved from thecontact of hot metal with the mold walls. Hence the presence of a largeamount of clay is not desirable.

A non-swelling montmorillonite clay, such as the non-colloidal PortersCreek clay described in my Patent Number2,123,404, or the colloidal clayset forth in my Patent Number 2,180,897,

is a satisfactory bonding material. The proportion of such a clayrequired to produce a mold having satisfactory green strength is onlyabout 5% of the weight of the sand. Thus a mold using a non-swellingmontmorillonite clay as a binder has satisfactory permeability to gases.A disadvantage of such a mold for some purposes is its low 'drystrength. Another disadvantage to consumers is that non-swellingmontmorillonite is found only in certain sections of the country,principally the central and south-central parts, and due to shippingcharges, use of it in other sections is expensive.

Another clay, which is a satisfactory bonding material, is a swellingcolloidal montmorillonite, containing approximately 20% of alumina(A1203). and 63% of silica (SiOa), known as'bentonite. This clay isfound in Wyoming and in other western states. Only a small percentage ofthis bonding agent need be used to produce a mold of requisite greenstrength. A disadvantage of bentonite as a moldbonding material is, formany purposes, the objectionably high dry strength given the mold.

I find ,that there are many casting operations which requiremolds ofintermediate dry strengths for best results. In my Patent 2,230,939 Ihave disclosed a bonding material satisfactory for such use, whichconsists of a blend of bentonite and non-swelling montmorillonite inproportions which will give any desired dry strength of mold.

As mentioned above, however, non-swelling montmorillonite is expensivein many sections of the country. In the western states, for example, itscost exceeds that of the locally produced bentonite. vIn suchlocalities, the use of the blended binder of my Patent 2,230,939 isprohibitively expensive.

Accordingly, an object of my invention is to provide a binder forfoundry compositions which is available in the western states and whichgives a desired dry strength in combination with high green strength,good permeance and other features enjoyed by molds using binders of thebentonitic clays.

In accordance with my present invention, I find that desired results arehad by treating Wyoming bentonite with an acid or acid salt in desiredamount. For this p pose, I use either an acid, such as hydrochloricacid, or an acid salt, for example potassium nitrate, sodium alum orammonium carbonate. One or more of these materials are readily availablein most localities. Since only a relatively small amount of one of thesematerials is required to achieve the desired result by my invention,their use is not expensive. This is particularly true because thematerials themselves are inexpensive.

I have found that when bentonlte is chemically treated with an acid oran acid salt and is then used as a bonding material, it imparts to themold a dry strength materially less than that resulting from the use ofuntreated bentonite alone. The dry strength of the mold varies inverselyas the amount of acid or acid salt blended with the bentonlte. Thus theresult of using a certain amount of treating material is definitelypredictable.

I have found that the same result will not follow where the salt used isbasic in nature. A basic salt mixed with bentonlte will cause the molddry strength to increase, rather than decrease, until an excess of suchsalt has been added, when the dry strength decreases.

The patent to Hanley No. 1,657,573 discloses that when bentonlte ismixed with sand and water each minute particle of the bentonite which isattached to any sand grain will swell up an appreciable extent andspread over the grain in the form of a sticky gelatinous film. This willcause each grain to effectively adhere to the adjacent grains withoutfilling up the spaces between them. A possible explanation for theaction of acid and acid salts on bentonlte is that they increase itsviscosity and thus reduce its spreading ability so that it does not bindas many rains of the sand as it does in its untreated condition. I donot desire, however, to be bound by this explanation.

In practicing my invention, an acid salt, such as potassium nitrate,sodium alum or ammonium carbonate, may be mixed with bentonlte when bothare in a dry condition before adding the bentonite to the sand. Equallygood results are achieved when the dry salts are added to the sand atthe same time the bentonite is mixed therewith. Another satisfactorymanner of introducing the salts is by dissolving them in the water usedto temper the sand. Still another method of treating the bentonite liesin using a dilute solution of inorganic acid, such as, hydrochloricacid, in place of the tempering water.

When acid salts are added in a dry condition, the bentonlte and salt aremixed in a. muller mixer, then are added to the sand in the proportionsof 95% sand and 5% binder and are mixed with it for one minute. As analternative method. the sand and bentonlte in the proportions of 95%sand and 5% bentonlte may be placed in a muller mixer together with thesalts and may be mixed dry for one minute. In either method, temperingwater is then added in suflicient amount .to give a moist workable mass,about 3% water generally being sufllcient, and the mixing is continuedfor four more minutes. The composition is then ready for use in a mold.

To compare the strengths of molds using treated and untreated bentonlterespectively as a binder, I prepared several dry mixing 95% sand and. 5%bentonite for one minute, then adding 3% tempering water and mixing forfour more minutes. I then conducted strength tests in accordance withrecommendations of the American Foundrymen's Association in its bookTesting and GradingEoundrySands and Clays,"published in 1938. Theresultant green and dry strengths of the molds containing treated anduntreated bentonite are given in the following table. The percentages ofsalt listed represent the proportion of the salt to the bentonlte byweight. The percentages of acid given represent the proportion of thevolume of concentrated acid to the volume of the tempering wateremployed.

Sand mold compositions Green com- Dry com- Bonding material pressionpression strength strength Lbs. per Lbs. 1m sq. in. sq. in. 5% untreatedbentonlte 7.64 76. 1

5% bentonlte plus- 1% potassium nitrate 7. 28 57. 4 2% potassium nitrate7. 32 50. 8 4% potassium nitrate i. 6. 69 41. 9

5% bentonite plusl% sodium alum 8. 16 67. 2 2% sodium alum 8. 52 64. 04% sodium alum 8. 70 57. 8

5% bentonite plus 1% ammonium carbonate 7. 77 62. 3 2% ammoniumcarbonate 8.15 53. 3 4% ammonium carbonate 7. 15 40. 5

5% bentonite lus- 3.33% by rochloric acid in water. 7. 96 73.1 8.33%hydrochloric acid in water 7. 43 40. 0 16.66% hydrochloric acid inwater.. 7. 29 32. 5

From an inspection of the above table, it will be seen that not only canthe dry strength be modified by adding certain amounts of acids or acidsalts but also that the green strength can be changed to some extent.Thus, a binder containing 4% potassium nitrate will produce a moldhaving a green compression strength of 6.69 pounds per square inch,whereas one containing 4% sodium alum will give a green strength of 8.70pounds per square inch.

Unlike untreated bentonite, my mold composition is easily handled. It isnot so gummy or sticky as ordinary bentonite. It flows freely. It isreadily rammed about a pattern using a conventional jolt machine. Thesand packs tightly about .the pattern. A smooth surface resultsacourately following the details of the pattern. The mold is strong anddurable. It is well retained in the cope as it is lifted from the dragto remove the pattern. The mold from which the pattern is withdrawn isclean-cut and free of edge breaks and cracks. A minimum of repair to themold before use, therefore, is required. At the same time, however, themold is porous and readily permeable to the fumes and gases encounteredin When the bentonite is treated by a dilute acid actual practical use.

Moreover, by using the method of my invention, it is easy to prepare amold having any desired strength. The amount of acid or salt which mustbe used for a certain mold strength is deflnitely predictable as thestrength varies inversely as to the amount of treating material used.

Furthermore, where a certain small percentage of treating material isused as herein outlined, the mold in a dry condition is not caked orhardened. Hence it is possible to recover the molding material by ascreening. operation for reuse in combination with clean sand.

By virtue of my invention, in any locality where bentonite clay isreadily available, that is in the western part of the country, aninexpensive 5 molding material can be prepared which is suitable for theparticular casting being made. For a heavy casting, such as a machinebase, bentonite alone or in combination with a. very small amount ofacid or salt is used as a binder, so that 1 the mold dry strength ishigh. Where an, intermediate dry strength is desired, for a mediumweight casting a larger percentage of acid or salt is used. Where thecasting is to be a light, thinwalled article, a mold of low dry strengthis de- 1 sired and for this purpose still more of the acid or salt isintroduced into the binder. When the mold strength is low, a thincasting can contract upon cooling without danger of being cracked by anunyielding mold part. The interior part of 2 a low strength moldcollapses upon cooling and thus allows unimpeded contraction of thecasting.

Thus, it will be seen that there has been provided in my invention acomposition and art of 2 employing thesame in which the various objectshereinbefore noted together with many thoroughly practical advantagesare successfully achieved. It will be seen that my bonding compositionis well adapted to withstand the many Although my invention has beendescribed in connection with a mold, it will be understood that it isalso applicable to other foundry uses. It is suitable for application tothe construction of cores and facing materials.

Furthermore, my bonding material may be used in combination with newsilica sand, burnt silica 4 sand, new molding sand, burnt molding sand,lake sand or bank sand. Also, small quantities of neutral auxiliarybinders, such as cereal binders, cement, g'oulac, pitch or rosin andcasting cleaning elements, such as sea coal, wood, flour 0r oils may 4be added.

While the amount of bonding material is illustratively given as about 5%of the weight of the sand with which it is mixed. it will be understoodthat good results are obtained when the amount r of bonding materialvaries from about 2% to 8% of the sand weight. In fact, theseproportions can be extended to to 8% where a part of the all reversibleincharacter and" that present in the burnt sand is called into play,thus decreasing the amount which need be added.

Similarly, while the acid salt added to the bentonite as given in thetable, amounts to some 1% to 4% of the bentonite used, I find that itfrequently is advantageous to extend this range from, say /2 to 10%byweight of bentonite. So, also, where an inorganic acldis employed, thismay range from some 1% to 25% by volume of tempering water.

As many possible embodiments may be made of my invention and as manychanges may be made in the embodiments hereinbefore set forth, it is tobe understood that all matter described herein is to be interpretedillustratively and not in a limiting sense.

What I claim is:

1. In a composition of matter of the class described, a foundrycomposition comprising in combination, sand, bentonite, and an aqueoussolution of hydrochloric acid.

2. In a composition of matter of the class described, a foundrycomposition comprising in combination sand, and one-half percent toeight percent of a bonding material, said bonding material consistingofbentonite treated with'a 1 aqueous solution of hydrochloric acid.

3. In preparing a composition for foundry purposes, the art whichconsists of dry mixing sand with to 8% bentonite by weight, temperingthe mixture with an aqueous lnlutlon of hydro- -chloric'acid, and mixingmaterials in a wet condition.

4. Inpreparing a composition for foundry purposes, the art whichconsists of mixing with sand a binder amounting to V2% to 6% by weightof the sand, the said binder comprising bentonite NORMAN J. nunnacx.

sand is burnt sand, since the bonding material isfl aqueous solution of

